Silicic acid

Silicic acid/sɪˈlɪsɪkˌæsɪd/ is the general name for a family of chemical compounds containing the element silicon attached to oxide and hydroxyl groups, with the general formula n. They are generally colorless and sparingly soluble in water. They are very weak acids, often polymeric, whose conjugate bases are the silicate ions.

Two important members of this class are orthosilicic acidH4SiO4 and the polymeric metasilicic acidn. No pure silicic acids have been isolated, but they exist in dilute water solutions (including seawater), and play important roles in biology and technology.

The silicon-oxygen double bond implied by the formula H2SiO3 is hypothetical or highly unstable, and the "silicic acid" above usually polymerizes and/or is further hydrated. For example,

or

Like other silanols, silicic acids are weak acids. Since no inorganic silicic acid has been purified, the reactivity of these species is inferred rather than observed. In concentrated solutions, generally silicic acids polymerize and ultimately degrade to silicon dioxide and water.